A Micro Electro-Mechanical System (MEMS) microphone may be formed by etching a pressure-sensitive diaphragm or acoustic sensor directly onto a silicon wafer via MEMS processing techniques. Layers of various materials are deposited on top of a silicon wafer and then the unwanted material is then etched away creating a moveable membrane and a fixed back plate over a cavity in the base wafer. The fixed back plate is a stiff perforated structure which enables the passage of air, while the membrane is a thin solid structure that flexes in response to changes in air pressure caused by sound waves. Thus, MEMS microphones have one sound inlet and a sealed back cavity, and the MEMS sensor measures the air pressure difference between the sound inlet and the back cavity.
The same numbers are used throughout the disclosure and the figures to reference like components and features. Numbers in the 100 series refer to features originally found in FIG. 1; numbers in the 200 series refer to features originally found in FIG. 2; and so on.